The present invention relates to cementing operations. More particularly, the present invention relates to cement compositions comprising improved fluid loss control additives, and methods of using such cement compositions.
Hydraulic cement compositions are commonly utilized in subterranean operations, particularly subterranean well completion and remedial operations. For example, hydraulic cement compositions are used in primary cementing operations whereby pipe strings such as casings and liners are cemented in well bores. In performing primary cementing, hydraulic cement compositions are pumped into the annular space between the walls of a well bore and the exterior surface of the pipe string disposed therein. The cement composition is permitted to set in the annular space, thereby forming an annular sheath of hardened substantially impermeable cement therein that substantially supports and positions the pipe string in the well bore and bonds the exterior surface of the pipe string to the walls of the well bore. Hydraulic cement compositions also are used in remedial cementing operations such as plugging highly permeable zones or fractures in well bores, plugging cracks and holes in pipe strings, and the like.
In some cases, subterranean formations may be unable to withstand the hydrostatic head pressure normally associated with fluids (e.g., cement compositions and the like) being injected into the formation. In such cases, the hydrostatic pressure may be sufficient to force such fluids into the permeable zones of the formation, which may result in a significant loss of fluid into the formation. This fluid loss into the formation is problematic for a number of reasons. For example, where the fluid loss occurs during a cementing operation, excessive fluid loss may cause a cement composition to be prematurely dehydrated, which may limit the amount of the cement composition that can be pumped and decrease the compressive strength of the cement composition. Excessive fluid loss into the formation also may prevent or reduce bond strength between the set cement composition and the subterranean zone, the walls of pipe, and/or the walls of the well bore.
In order to counteract these problems, fluid loss control additives may be added to cement compositions to reduce the loss of fluid from the cement compositions when they contact permeable zones of the subterranean formation. Fluid loss control additives also may be suitable for cement compositions used in surface cementing operations. Conventional synthetic fluid loss control additives may be high molecular weight, water-soluble polymers, such as copolymers and copolymer salts of N,N-dimethylacrylamide and 2-acrylamido-2-methylpropane sulfonic acid. While these conventional fluid loss control additives have been used with some success, there is a continuing need for improved fluid loss control additives that achieve fluid loss control in well cement compositions.